Objectives #1-2: Introduction to Chemical Bonding

Objectives #1-2: Introduction to Chemical

BondingI. The Bonding Process

Chemical bonds form so as to lower the energy of each atom involved in the bond

Usually only involves the valence electrons in atoms

During the bonding process, electrons are shared or transferred in such a way so that each atom involved achieves the electron configuration of a noble gas!

Formation of H-H Bond Lowers Energy

Formation of the Noble Gas Configuration Through Bonding

II. Types of Chemical BondsA. Ionic Bond

Involves the transfer of valence electrons from a metal to a nonmetal

Formula units are formed, NOT molecules!B. Pure Covalent aka Nonpolar Covalent Bond

Involves the equal sharing of valence electrons between nonmetallic atoms

Molecules are formedC. Polar Covalent Bond—Polar Bears!!

Involves the unequal sharing of valence electrons between nonmetallic atoms

Polar molecules generally are formed, but there are exceptions!Example diagrams:

Objectives #1-2: Introduction to Chemical

Bonding

Formation of Ionic BondExplain the differences in the ion size, based on trends... Note also that each ion charge is a result of transferring electrons! The formula unit is the lowest ratio of positive & negative charges needed to form the bond.

Formation of Nonpolar Bond

Note that only the SHARED electrons will form a new molecular orbital. Since atoms are of equal size, the shared elec. will spend equal time around each nucleus.

Formation of Polar BondNote that electrons are not distributed equally in this molecule, (as shown by the d-) so there will be areas that always have more of a negative charge than the central atom of sulfur. If the dipole is strong enough, it can influence the electron distribution of neighbouring molecules.

Objectives #1-2 Introduction to Chemical

BondingIII. Determining Expected Bond Type Through

Electronegativity Differences in the electronegativity values of the

atoms that bond together determine the type of bond that forms between them

The following scale is used to determine expected bond type:

0.0 - 0.3 Nonpolar (low ionic character) 0.3 – 1.7 Polar Covalent 1.7 – 4.0 Ionic (high ionic character) Examples: H and H N and H F and F Ca and O

Table of Electronegativities

Objectives #3-4: Lewis Structures and Covalent Bonding

I. Energy and Bonding Once the repulsive forces between atoms are

overcome, a stable bond between nonmetals can form

Bond formation decreases the overall energy of the atoms involved in the bond

The strength of a covalent bond can be expressed in its bond energy; the greater the bond energy the stronger the bond will be; this same energy is also needed to break the bond

As the bond length between two atoms increases the bond energy decreases

Effects of Repulsive Forces on the Formation of a Chemical Bond

Bond Length vs. Bond Energy

**Note that the bond length is a function of the number of electrons being shared between the atoms! Double and triple bonds have a shorter bond length & require more energy to break.

Objectives #3-4: Lewis Structures and Covalent Bonding

II. Drawing Lewis Structures General formula : ExamplesIII.Single Covalent Bonds Single covalent bonds involve the

sharing of 1 pair of electrons Steps to drawing Lewis structures for

molecules:1. Add up the # of valence electrons

Objectives #3-4: Lewis Structures and Covalent Bonding

2. Place lone atom in the center3. Use single bonds to form bonds; complete

octets or duets as needed with lone pairs4. If valence count is exceeded, reduce

number of lone pairs and use multiple bonds

Lone pairs vs. Bonding pairs: lone pairs occupy regions of molecule where bonds are not present in order to complete octets; help determine shape

Single Bond Examples:

Objectives #3-4: Lewis Structures and Covalent BondingRepresentations for Covalent Substances: Molecular Formula:

Complete Structural Formula:

Condensed Structural Formula:

IV.Formation of Double Bonds Double covalent bonds involve the sharing

of 2 pairs of electrons Examples

Objectives #3-4: Lewis Structures and Covalent Bonding

V. Formation of Triple Bonds Triple covalent bonds involve the

sharing of 3 pairs of electrons Examples:

Objectives #3-4 : Lewis Structures and Covalent Bonding

VI.Other Types of Organic Functional Groups

The functional group is the chemically active site on a carbon containing organic molecule

Functional Group Class Name Example-OH Alcohol CH3CH2OH

-X (halogen) Alkyl halide CH3Cl

-O- Ether CH3OCH3

-CHO Aldehyde CH3CHO

-CO Ketone CH3COCH2CH3

-N Amine CH3CH2NH2

-COOH Carboxylic acid CH3CH2COOH

-COOC Ester CH3CH2COOCH3

Objectives #5-7 Formation of Ions / Formation of Ionic Bonds / Properties of Ionic vs. Covalent

SubstancesI. Applications of the Octet Rule in

Ionic BondingA. Formation of Cations*metals achieve octets by losing

electronsB. Formation of Anions*nonmetals achieve octets by gaining

electrons*examples of cation and anion

formation:

Objectives #5-7 Formation of Ions / Formation of Ionic Bonds / Properties of

Ionic vs. Covalent Substances

II. Formation of Ionic Bond*the product of ionic bonding is the

formation of a formula unit which shows the chemical formula of the compound in its lowest terms

*the arrangement of ions in an ionic crystal is called the crystal lattice

Objectives #5-7 Formation of Ions / Formation of Ionic Bonds / Properties of Ionic vs. Covalent

Substances

*energy changes needed to form crystal lattice: (NaCl)

1. Formation of cation Na › Na+1 + e-

addition of I.E., endothermic2. Formation of anion Cl + e- › Cl-1

removal of E.A., exothermic3. Formation of crystal lattice NaClremoval of lattice energy, exothermic

III. Characteristics of Ionic and Covalent Substances

Characteristic Covalent Compounds

Ionic Compounds

Intramolecular Forces

Strong Strong

Intermolecular Forces

Weaker Stronger

State of Matter Mainly gases and liquids

Solids

Melting Point Low HighBoiling Point Low HighHardness Low Hard but brittleConductivity Some are Many are

IV. Crystalline Solids

*solids usually exist as two types; amorphous solids which lack a definite crystalline structure such as wax or glass and crystalline solids which contain a definite crystalline structure called a crystal lattice such as in sodium chloride

*the four major types of crystal structures and their properties are as follows:

Crystal Type Description of Structure

Properties and Example

Ionic Crystal + and – ions arranged in a regular pattern

hard, brittle, high melting points, good insulators (NaCl)

Covalent Network Crystals

a network of covalently bonded atoms forming giant molecules

hard, brittle, high melting points, nonconductors or semiconductors (sand, diamond)

Metallic Crystals metal cations surrounded by electron sea

malleability and high conductivity

Covalent Molecular Crystals

covalently bonded molecules held together with intermolecular forces

low melting points, soft, good insulators

Example of Ionic Crystal

Example of Covalent Network Crystal

Example of Metallic Crystal

Covalent Molecular Crystal

Objectives #8-9 VSEPR Theory and Molecular Polarity

*steric number is the sum of the number of atoms attached to the central atom plus the number of lone pairs attached to the central atom

*examples:*relationship of number of lone pairs and

resulting bond angles: as the number of lone pairs on the central atom increases the bond angle decreases

Objective #10 Intermolecular Forces

*intermolecular forces vs. intramolecular forces: attractive forces that operate between molecules

A. London Dispersion Forces*involves interactions between nonpolar

moleculesB. Dipole-dipole Interaction Forces*involves interactions between polar

molecules

Objective #10 Intermolecular Forces

C. Hydrogen Bonding Forces*involve interactions between polar

molecules and the element hydrogen; usually only involves polar molecules containing the elements F, O, and N

*diagrams and examples of intermolecular forces:

Objective #10 Intermolecular Forces

D. Influence of Intermolecular Forces on Boiling and Melting Points

(examples)